Brush retainer for rotating electrical machines



April 1955 w. E. BURCHFIELD 2,705,261

BRUSH RETAINER FOR ROTATING ELECTRICAL MACHINES Filed April 16. 1954 2 Sheets-Sheet PRIORART FIG.IA FIG. IB FIG. IO

FIG. 2C

VENTOR WILLARD F. B GHFIELD ATTORNEY April 12, 1955 w. F. BURCHFIELD 2,706,261

BRUSH RETAINER FOR ROTATING ELECTRICAL MACHINES Filed April 16, 1954 2 Sheets-Sheet 2 Fig. 3 he. 4

INVENTOR. WILLARD E BURCHFIEU) ATTORNEY United States Patent BRUSH RETAINER FOR ROTATING ELECTRICAL MACHINES Willard F. Burchfield, Hudson, Ohio, assignor to Jack &

Heintz, Inc., Cleveland, Ohio, a corporation of Delaware Application April 16, 1954, Serial No. 423,605 4 Claims. (Cl. 310246) This invention relates in general to rotating electrical machines and more particularly to electrical brushes and brush retainers.

One of the primary objects of my invention is to provide split brushes with an improved retainer which will not only provide a surface for the brush spring to rest upon, but also to allow independent axial action of each half of the split brush so as to enable the two halves of the split brush to maintain constant contact with the commutator segments even during engagement with commutator segment surface irregularities, so as to increase the sliding and commutating qualities of the brushes by enabling the brushes to ride smoothly on the contour of the commutator when high, low, or uneven commutator segments are encountered.

Another object of my invention is to provide a split brush retainer that will enable the brushes to seat evenly over the entire brush surface with a minimum of run-in time required as compared to conventional split brushes equipped with conventional solid clip retainers WhlCh do not allow independent motion of the brush segments as in the case of uneven commutator surfaces.

A further object is to provide a brush retainer that will improve the riding characteristics of these brush segments and make it possible to reduce the spring pressures necessary for proper commutation and thus reduce the wear rate of the brushes.

With the foregoing and other objects in view, the invention resides in the combination of parts and in the details of construction set forth in the following specification and appended claims, certain embodiments thereof being illustrated in the accompanying drawings, in which:

Figures 1A, 1B and 1C are views in front elevation, rear elevation and vertical section taken through a split brush and conventional retainer clip;

Figures 2A, 2B and 2C are views in front elevation, rear elevation and a vertical section taken through a split brush and my improved retainer clip;

Figure 3 is a schematic view in section of a conventional split brush and clip assembly engaging a commutator in rotation, showing the trailing brush in engagement with a high commutator surface;

Figure 4 is a schematic view of a conventional split brush and clip assembly engaging a commutator in rotation, showing the leading brush in engagement with a high commutator segment and an air gap between the trailing brush and the commutator surface;

Figure 5 is a schematic view, similar to Figure 3, showing my improved split brush and clip assembly with the trailing brush in engagement with a high commutator segment and the leading brush in engagement with a normal height segment of a rotating commutator; and

Figure 6 is a schematic view, similar to Figure 4, showing my improved split brush and clip assembly, with the leading brush in engagement with the high commutator segment and the trailing brush in engagement with the normal height segment of a rotating commutator.

Referring more particularly to the drawings, and in order to more clearly define the improvements in the art afforded by my invention, I have shown in Figures 1A, 1B and 1C, the conventional split brush and retainer clip assembly. This includes a split brush unit with brushes 1 and 2 with regular bottom surfaces for engagement with commutator segments and upper surfaces 3 and 4 that are chamfered to be inclined downwardly from right to left. The usual electrical leads 5 and 6 are held in place in the split brush by a rivet 7. As shown, the

usual practice is to employ a unitary spring metal clip 8 secured to brush 1 by a rivet 9. The upper portion of the solid unitary spring clip 8 is bent angularly downwardly from right to left at 10 to match and engage both chamfered surfaces 3 and 4 in the top slot 11 in brush 2. This maintains brushes 1 and 2 in flatwise surface engagement. It also resiliently, but positively, maintains the lower ends of the brushes in horizontal alignment and the brushes against relative sliding displacement in one direction. In further explanation, it will be noted that whereas in this construction the brush 2 is not secured to the brush clip 8, in the event of a surface irregularity of the commutator on which the brush rides, the two brushes would tend to operate in unison much like a solid one-piece brush because of the spring clip 8 not being hinged and thus prevents brush 2 from rising independently of brush 1. This is illustrated in Figures 3 and 4, wherein I have shown a fractional portion of a commutator 12 rotating in a clockwise direction, as indicated by the arrow. In both Figures 3 and 4, I have shown a high commutator segment 13 that protrudes radially outwardly a nominal amount beyond the two adjacent commutator segments 14 and 15 on either side thereof. It should be pointed out that in most cases this diiferential may not exceed .001 inch and in some cases as little as .0002 inch. These values, however, are sufiicient to cause distress, particularly in high rotative speeds of the commutator shown. The high segment 13, in passing under brush 1 in Figure 3 shows how the whole split brush is lifted up, since the clip is rigidly attached to the trailing brush 1. Under this condition of operation, the leading brush 2 may assume the position shown where there occurs an air gap 16 between brush 2 and commutator. This is because the downwardly applied force of brush spring 23 on clip 10 is not transmitted to brush 2, because clip 10 is rigid and not pivoted. The brush spring 23 may be carried by the brush holder 24. Thus, the contact of the split brush with the commutator is insufficient to carry the proper amount of current and also does not cover the proper amount of arcuate surface of the commutator. Figure 4 shows the high commutator segment 13 under the leading brush 2, and the trailing brush 1 bodily raised from the surface of commutator segment 15 through the unpivoted rigid slip, to leave an air gap 18 therebetween. In this condition, the above difiiculties described for Figure 3 are ap-:

plicable. In addition, as the high commutator segment 13 passes from contact with brush 1, there is momentarily no brush actuating pressure due to mass inertia of the brush with the resulting contact interruption between both brushes and the commutator face. This condition, in turn, will tend to produce an arc, resulting in burning or. eroding the commutating surface.

In order to remedy this condition, I the clip 8 with an improved type of in Figures 2A, 2B and 2C, 5 and 6. To brush 1, I secure a plate 18 by means of a rivet 10. Plate 18 has an aperture 20 to loosely receive a leaf 21 which rests on the upper surfaces 3 and 4 of brushes 1 and 2 and also loosely in groove 11 in upper surface 4 to avoid undue relative side play between the brushes. The leaf 21 is provided with a hook 22 which loosely retains the leaf in aperture 20 of plate 18 so as to permit free pivotal movement of the leaf. This permits relative vertical sliding movement between the two brushes 1 and 2 in both vertical directions, as distinguished from the spring clip 8, which permits relative vertical sliding movement in one direction only. Since the brush retainer leaf 21 and the supporting plate 18 are secured by means of a loose hinge type joint 22, the brush retainer leaf 21 may change its angle with the axis of brush 2 by a limited, but sufficient, amount to maintain a pressure between the split brush and commutator segments at all times. Thus, the spring force applied vertically by brush spring 23 is divided between the two brushes under all conditions of operation.

Figures 5 and 6, which are representative of my invention, as shown in Figures 2A, 2B and 2C, illustrate the advantages gained by having independent axial action of each brush 1 and 2. This allows brush contact to be maintained with the commutator surface the maximum propose to replace retamer, as shown amount of the time, as shown in Figure 5, unlike that of Figure 3, when high commutator segment 13 passes under brush 1. The brush 2, in this case, remains in contact with commutator surface, by contact with commutator segment 14, as the result of my improved floating hinge type retainer, which allows spring 23 to exert sufficient pressure on brush 2 to insure its contact with the commutator surface at all times.

I have found, as stated previously, that split brushes provided with my improved retainer, have superior sliding and commutating qualities which are exemplified by the ability of these brushes to ride the contour of the commutator when high, low or uneven bars are encountered. Furthermore, due to the improved brush riding and commutating characteristics, the commutator surface is not subjected to burning or eroding because of the aforementioned continuity of current carrying contact. My floating retainer tends to distribute the brush spring tension between the two brushes at all times so as to maintain a positive resilient force on each of the two brushes on the commutator. Commutation is greatly improved on machines utilizing this hinge type floating brush retainer, as evidenced by a substantial improvement in the ability to commutate without sparks at high rotative speeds and high electrical loads. Because of the continuity of the spring brush pressure on the commutator, the run-in time for obtaining proper seat between the brush and commutator is substantially reduced. Because -of the uniform spring pressure of the brush on the commutator, the tendency of arcs to occur between the brush segments and commutator segments is reduced, thus reducing tendency to pit and erode the commutator surface. This latter effect means that a smooth surface and proper commutator protective film may be maintained longer and more effectively, resulting in improved commutation and longer brush life, when irregular commutator segments are encountered.

I claim:

1. In combination in a rotating electrical machine commutator having a plurality of segments, a brush holder and a split brush comprising a pair of brushes, a retainer hingedly connected to one of said brushes and overlapping the other brush for maintaining said two brushes in flatwise surface contact with each other, a brush spring mounted on said brush holder and extending to slidably bear resiliently on the upper surface of said retainer, the bottom surfaces of said brushes being adapted to engage the outer surfaces of said commutator segments under the resilient pressure of said brush spring on said hinged retainer to permit limited relative radial sliding movement between said brushes in both directions, under urging of said brush spring, whereby constant uninterrupted commutator contact is maintained by both brushes, regardless of the relative unevenness in the radial outside dimensions of said commutator segments.

2. In combination in a rotating electrical machine commutator having a plurality of segments, a brush holder and a split brush comprising a pair of brushes, a retainer for maintaining said two brushes in flatwise surface contact with each other, the bottom surfaces of said brushes being adapted to engage the outer surfaces of said commutator segments, said retainer including a leaf loosely hingedly connected to one of said brushes so as to constitute a free floating pivotal connection between said retainr leaf and said last named brush and overlapping the other brush to permit unopposed relative radial sliding movement between said brushes in both directions, a brush spring secured to said brush holder and extending to slidably bear radially inwardly on said retainer leaf under equal resilient pressure, whereby constant uninterrupted commutating contact with said commutator is maintained by both brushes under the urging of said brush spring, regardless of the relative unevenness in the radial outside dimensions of said commutator segments.

3. In combination in a rotating electrical machine commutator having a plurality of segments, a brush holder and a split brush comprising a pair of brushes, a retainer for maintaining said two brushes in flatwise surface contact with each other, the bottom surfaces of said brushes being adapted to engage the outer surfaces of said commutator segments, said retainer including a supporting plate secured to one of said brushes, a retainer leaf extending loosely through an aperture in said supporting plate and having a hooked end to constitute a free floating pivotal connection and overlapping the other brush to permit unopposed relative radial sliding movement between said brushes in both directions, a brush spring carried by said brush holder and extending to slidably bear resiliently radially inwardly on said leaf to urge both of said brushes radially inwardly toward said commutator under equal resilient pressure, whereby constant uninterrupted commutating contact with said commutator is maintained by both brushes, regardless of the relative unevenness in the radial outside dimensions of said commutator segments.

4. In combination in a rotating electrical machine commutator having a plurality of segments,a brush holder, and a split brush comprising a pair of brushes, each brush having an electric lead, a retainer for maintaining said two brushes in flatwise surface contact with each other, the bottom surfaces of said brushes being adapted to engage the outer surfaces of said commutator segments, said retainer including a supporting plate secured to one of said brushes, a guide slot in the upper surfaces of said brushes and a retainer leaf extending loosely through an aperture in said supporting plate and having a hooked end to constitute a free floating pivotal connection and overlapping the other brush to permit unopposed relative radial sliding movement between said brushes in both directions, a brush spring carried by said brush holder and extending to slidably bear resiliently radially inwardly on said pivoted leaf to urge both of said brushes radially inwardly toward said commutator under equal resilient pressure, whereby constant uninterrupted commutator contact is maintained by both brushes, regardless of the relative unevenness in the radial outside dimensions of said commutator segments.

References Cited in the file of this patent UNITED STATES PATENTS 828,528 Thomas Aug. 14, 1906 2,488,788 Weilbaecher Nov. 22, 1949 2,520,379 Ward Aug. 29, 1950 

